From: Allen Minton <minton@helix.nih.gov>
  To  : rasmb@bbri.harvard.edu
  Date: Thu, 06 Sep 2001 16:41:52 -0400

hydrodynamic question

Hi gang -

A question for the hydrodynamics experts:

We can calculate the frictional coefficient for an ellipsoid of rotation 
(prolate or oblate) using the well-known Perrin equation.   How can we 
calculate the frictional coefficient for a cylindrical rod of arbitrary 
length/diameter ratio?

I am guessing that the bead model might work, but it's not clear how one 
would best represent the rod as an array of beads.  I doubt that one could 
realistically represent the rod as a simple linear array of beads with a 
diameter equal to a bead diameter and a length equal to the number of beads 
times the bead diameter, but perhaps some experienced person could set me 
right on that point.

Does anyone know of an analytical solution to the rod problem, along the 
lines of the Perrin equation?

Allen Minton